Commercially available (Ed. Geistlich Sons Ltd.) porcine collagen film (Geistlich 1 and 2) have been analysed and found to contain the following on a dry weight basis:
Geistlich 1Geistlich 2Collagen48.7%68.8%Glycerol19.7%20.6%Fat30.6%12.4%Ash 0.7% 0.4%Collagen:Fat Ratio1.6:15.5:1
Throughout these examples, the weight percentages will approximate 100% but within the limits of experimental error.
Defatting
The raw material is normally received as a salted pig (sow) skin (hide).
A typical defatting process would involve some or all of the following steps:    1. Initial Soak—Add the skins to the processing drum and add between 150% to 200% equivalent weight of fresh clean water at 28 deg C. Rotate for up to 1 hour and drain the vessel.    2. Main Soak—Add water (28 to 32 deg C.) equivalent to 100% to 200% weight of raw hides. Add up to 0.5% of sodium carbonate or the like (helps to rehydrate through elevating the pH) and up to 0.2% by weight of wetting agent such as Danol WA (helps rehydration and removal of surface fats).    3. Fat removal—Remove hides from the vessel. Feed the whole hide pieces into a proprietary fleshing machine such as those made by Poletto, Rizzi, Mosconi & Persico. Set the cutter height to an appropriate position to effect good visual fat reduction without unduly removing good collagen. Fat removal can also be done prior to the soaking stages using a suitable proprietary fleshing machine. Hides prepared in such a manner are usually shipped in a salted condition but can also be frozen without use of salt. Material prepared in such a fashion can proceed to unhairing straight away after completing the initial soaking stages.    4. Unhair-Reweigh material into vessel. Add water (about 25 deg C.) at up to 200% equivalent weight of hides. Add up to 3.5% by weight of sodium sulfide or up to 5% by weight of sodium hydrosulfide, and a wetting agent at up to 0.2% by weight. A strong alkali is usually added, such as sodium hydroxide or lime to maintain the pH at 11 to 12 for the duration of the processing time. A liming auxiliary such as Erhavit MC or Aglutan PR at up to 0.3% by weight is usually added also. Typical processing times are between 12 hours and 60 hours before the liquor is drained.    5. Wash 1—Add fresh clean water (200% equivalent weight) along with a wetting agent (typically 0.2%) and rotate for 30 minutes then drain.    6. Wash 2—Add fresh clean water (200% equivalent weight) and rotate for up to 30 minutes then drain. This stage can be repeated up to 4 times to remove residual surfactant (until no evidence of foam in the vessel).    7. Decalcification—Remove excess calcium ions (only where lime was previously used) with ammonium sulphate solution to a pH of around 9.    8. Buffer—Reduce pH of hides to around 2.5 to 6 with a solution of citric acid and sodium citrate, or hydrochloric acid.    9. Final washes—Wash hides with batches of fresh clean water to remove dissolved salts to a level where the drained liquor conductivity falls below 200 μmhos.